Area variation in the use of surgical interventions such as arthroplasty is viewed as concerning and inappropriate. To determine whether area arthroplasty rates reflect patient-related demand factors,  the need for and the willingness to undergo arthroplasty in a high- and a low-use area of Ontario, Canada was estimated using a population-based mail and telephone survey. All adults aged 55 years or older in a high (n = 21,925) and low (n = 26,293) arthroplasty use area were eligible for the study. Arthritis severity and comorbidity was determined with questionnaires, established the presence of arthritis with examination and radiographs, and evaluated willingness to have arthroplasty with interviews. Potential arthroplasty need was defined as severe arthritis, no absolute contraindication for surgery, and evidence of arthritis on examination and radiographs. Estimates of need were then adjusted for patients' willingness to undergo arthroplasty. The potential need for arthroplasty was significantly different between the high and low rate areas (36.3/1,000 vs 28.5/1,000 respectively). Among individuals with potential need, only 14.9% in the high-rate area and 8.5% in the low-rate area were definitely willing to undergo arthroplasty, yielding adjusted estimates of need of 5.4/1,000 and 2.4/1,000 in the high- and low-rate areas, respectively. Demonstrable need and willingness were greater in the high-rate area, suggesting these factors explain in part the observed geographic rate variations for this procedure. Among those with severe arthritis, no more than 15% were definitely willing to undergo arthroplasty, emphasizing the importance of considering both patients' preferences and surgical indications when evaluating need and appropriateness of rates for surgery.